Note: Descriptions are shown in the official language in which they were submitted.
~"~S7~52
PULSE CLEANING SYSTEM FOR DUST FILTERS
This invention relates in general to the filtration of
dust laden gases and more particularly to a bag type dust
filter having an improved system for cleaning of the
filter bags.
In bag type dust filtration equipment, dust laden air is
passed through a bank of filter bags which remove the
dust. In this particular type fi]ter, the bags are
normally suspended from a tube sheet located between an
underlying dirty air plenum and an overlying clean air
plenum. The dust laden air is drawn into the dirty air
plenum and through the filter bags into the clean air
plenum from which the filtered air is discharged. The
dust which is removed from the air collects on the outside
surfaces of the filter bags and must be periodically
dislodged to maintain the bags in condition to effectively
perform their filtering function. When the filter housing
is cylindrical, cleaning of the filters is often performed
by a rotating arm which applies pulses of reverse flowing
air through the bags to remove the accumulated dust.
This type of cleaning system is generally shown in U.S.
Patent No. 4,157,899 to Wheaton.
Cleaning of the filter bags with a radial cleaning arm
presents a number of difficulties which are caused in
part by the geometry. The cleaning arm normally has a
single row of discharge nozzles for applying the air
pulses. However, it is not desirable to arrange the
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61316-613
fi.lter bags in rows extending along radial lines on the tube shest
because this type of arrangement æpaces the bags in the outer
rings so far apart that effective use of the tube sheet area is
not made. If the filter bags are arranyed to achieve efficient
filtration, they are not located on common radial~ and the
cleaning arm is not able to clean all of the filters in a uniform
manner. If air is applied to the cleaning arm while some of its
discharye nozzles are misaligned with the underlying bags, at
least some of the cleaning air is wasted because it is directed
against the surface of the tube sheet where it does no good. ~Ihen
the air is discharged randomly from the arm, the effectiveness of
the cleaning air application to any one bag is purely a matter o~
chance, and the uniformity of the cleaning operation suffers
accordingly.
Flow losses have also ~etracted from the cleaning efficiency. The
cleaning air is typically accumulated in a tank that may be
located some distance from the cleaning arm. Because of the
distance the compressed air must travel between the tank and arm,
there are signiflcant flow losses. The distance between the
accumulator tank and the cleaning arm also increases the response
time of the system, resul~ing in a delay between opening of the
main valve and application of the cleaning air pulses to the
filter bags.
The present invention provides a pulse cleaning system in which
the air accumulator tank is located adjacent to the cleaning arm
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in order to decrease both the response time and the flO~r~ losge3.
At the same time, the cleaning operation is accurately controlled
to apply equal pulses to all filter bags at the same frequency so
that uniform ~leaning of all bags is assured.
In accordance with the invention, there is ~rovided in gas
filtering apparatus having dirty and clean air chambers separated
by a generally horizontal partition presenting a plurality of
openings each provided with a filter bag, an improved bag cleaning
arrangement comprising: an upright air accumulator tank for
receiving and accumulating a supply of air under pressure; means
for mounting said tank in the clean gas chamber for rotation about
a substantially vertical axis; drive means for rotating said tank
about said axis; means for supplying air under pressure to said
tank as same is rotating; a substantially horizontal air
distribution arm extending from said tank and rotating there~Jith
in a path carrying said arm over the partition said tank providing
the sole source of air flow to said arm; a plurality of outlets
spaced along said arm for discharging air therefrom in pulses,
said outlet being located to suc~essively align with openings in
the partition as said arm rotates; valve means for controlling the
~low of air from said tank into said arm, and valve control means
for intermittently opening and closing said valve means to allow
air from the tank to enter the arm in a pulse each time said valve
means is opened and to allow air to accumulate in the tank during
the intervals said valve means is closed, where~y air in the tank
flo~7s into said arm and discharges in pulses through said outlets
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61316-~13
and into the filter bags ~o dislodge dus~ therefrom each time said
valve means is opened.
Preferably the partition or the tube sheet is divided into
identical pie shaped segments, and each
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segment has its filter bag openings arranged in the same
pattern. The discharge nozzles on the radial cleaning arm
are arranged in a pattern which is identical to the
pattern of the filter bags on each segment of the tube
sheet. As the cleaning arm rotates, it is aligned
above the successive segments and all of its nozzles are
directly centered on all of the filter bags on the
underlying segment when the cleaning pulses are applied.
Consequently, all of the cleaning air is used effectively
to clean the filters, and the filters are uniformly
cleaned because each filter bag receives a pulse applied
with the same force and frequency as the pulses applied to
all other bags.
Another important feature of the invention is the
location of the air accumulator tank and main valve
adjacent to the cleaning arm. The tank is mounted in the
clean air plenum for rotation about an axis coincident
with the center of the tube sheet, and the tank thus
serves as a structural part of the rotation system for
the arm. A large gear is mounted on top of the tank and
is driven by an electric drive motor to rotate the tank
and the connected cleaning arm at a constant speed. A
stationary supply line continuously supplies compressed
air to the rotating tank through a rotary union which
also uniquely accommodates a pilot line controlled by a
solenoid valve. Flow from the tank into the cleaning arm
is controlled by a diaphragm valve which is in turn
controlled by a secondary valve that the solenoid valve
opens and closes in accordance with the rotational
position of the arm. The valve system is quick acting and
is located as close as possible to the cleaning arm so
that flow losses and response time are minimized~
The control system includes a position sensor which
provides a signal each time the cleaning arm is aligned
directly above one of the segments of the tube sheet. As
an example, the solenoid valve is preferably actuated each
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time three signals are generated in order to provide
sufficient time for the necessary pressure to build up in
the accumulator tank and to reduce adjacent bag
redeposition of dust. When the solenoid valve is
S actuated, it opens the secondary valve and the main
diaphragm valve in rapid succession to apply air pulses
through the cleaning nozzles while they are exactly
centered on the underlying filter bags. This exact
alignment between the nozzles and filters assures
efEective use of every air pulse. At the same time,
the filter bags are cleaned uniformly because each bag
receives one cleaning pulse for every three revolutions of
the cleaning arm. The number of signals generated prior
tp pulsing can be varied, depending on the air filter size
and configuration.
In the accompanying drawings which form a part of the
specification and are to be read in conjunction therewith
and in which like reference numerals are used to indicate
like parts in the various views:
Fig. 1 is a fragmentary sectional view taken on a vertical
plane through a dust filter equipped with a pulse cleaning
system constructed according to a preferred embodiment
of the invention, with portions broken away for purposes
of illustration;
Fig. 2 is a sectional view taken generally along line 2-2
of Fig. l in the direction of the arrows;
Fig. 3 is a fragmentary sectional view on an enlarged
scale showing the gear drive arrangement and related
components near the top end of the air accumulator tank;
Fig. 4 is a fragmentary view taken generally along line 4-
4 of Fig. 3 in the direction of the arrows;
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Fig. 5 is a fragmentary elevational view on an enlarged
scale showing the main diaphragm valve and related part.s
of the pulse cleaning system, with the diaphragm in the
closed position and portions broken away for purposes of
illustration;
FigO 6 is a fragmentary view similar to Fig. 5, but
showing the diaphragm in the open position; and
Fig. 7 is a diagrammatic view of the control box for
the pulse cleaning system.
Referring now to the drawings in more detail and initially
to Fig. 1, numeral 10 generally designates a bag type dust
filter. A sheet metal housing 12 has a cylindrical
configuration and may be supported by suitable support
legs (not shown). A circular tube sheet 14 is secured at
its periphery to the housing 12 and forms a horizontal
partition which divides the housing 12 into two chambers
or plenums 16 and 18. The plenum 16 located above the
tube sheet is referred to as a clean air plenum, and the
plenum 18 below the tube sheet is referred to as a dirty
air plenum. A conical hopper (not shown) is normally
provided on the bottom of the dirty air plenum 18 for
collection of the dust that i5 removed during
operation of the dust filter 10. An auger or other
conveyor system (also not shown) conveys the dust away
from the collection hopper. An access door 20 (see Fig.
2) in the side of housing 12 provides access to the clean
air plenum 16.
As best shown in Fig. 2, the circular tube sheet 14 is
divided into a number of adjacent pie shaped segments
22. Each segment 22 is bounded by a pair of radials 24
extending from the center of the tube sheet and a
chord 26 on the periphery of the tube sheet. All of tne
segments 22 are identical in size and shape. There are
twenty five segments in the embodiment of the invention
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shown in Fig. 2, although different numbers can be
selectedO
A plurality of openings 28 are formed t'nrough t'ne tube
5 sheet 14 and are arranged in a plurality of concentric
rings centered at the center of the tube sheet. Each
opening 28 receives a filter bag 30 formed by a fabric bag
fitted on a cage 32 (see Fig. 1) which provides skeletal
support for the fabric bag. An enlarged collar 34 is
10 provided on the top end of each filter bag 30 and
rests on the top surface of the tube sheet 1~ to suspend
the bags 30 from the tube sheet. The filter bags 30
extend from the tube sheet into the dirty air plenum 18
and serve to filter dust from the dust laden air which
15 passes from 'che dirty air plenum 18 into the clean air
plenum 16.
Each segment 22 of the tube sheet has the same number of
openings 28, and the openings are arranged on each segment
20 in the same pattern, which is shown in Fig. 2. At the
locations of several of the inner concentric rings of
openings 28, the segments 22 are wide enough to
accommodate only a single opening 28 and associated filter
bag 30. The segments are wider at the locations of the
25 outer rings, and each segment is provided with two or
more openings 28 at the locations of the outer rings of
openings. The outermost set of openings in each segment
22 includes three openings 28. Each segment 22 is
preferably provided with as many openings and filter bags
30 as possible while still accommodating the arrangement
of the openings in concentric rings and maintaining
adequate space between adjacent openings. It is to be
understood that patterns different from that shown in Fig.
2 are possible.
In accordance with the present invention, an air
accumulator tank 36 is mounted for rotation in the clean
air plenum 16. Tank 36 serves as a reservoir for the
7 ~257~
compressed air which is used to clean the filter bags
30O Tank 36 has a generally cylindrical body, and its
axis of rotation passes centrally through the tank and
coincides with the center of the circular tube sheet 14.
A bearing 38 is mounted on the center of the tube
sheet and receives a short shaft 40 projectiny fr~m the
bottom of the air accumulator tank 36.
As shown in Fig. 3, air is applied to the accumulator tank
36 through an inlet pipe 42 extending centrally from
the top of the tank. At its top end, pipe 42 is secured
to a circular peg wheel 44. A large gear 46 overlies the
peg wheel 44 and is separated therefrom by a thin spacer
disk 48. A rotary union 50 has a cylindrical outer body
52 which is flanged at its lower end and secured by
bolts 54 to the gear 46, spacer 48 and peg wheel 44. Body
52 receives and rotates on a somewhat smaller sleeve 56
which is flanged on its top end and bolted at 58 to a
rectangular mounting plate 60. The mounting plate 60 is
in turn mounted on a pair of parallel channels 62
which extend across the housing 12 and are secured thereto
at their opposite ends, as best shown in Fig. 2.
Referring again to Fig. 3, a bronze bushing 64 is
interposed between the rotating body 52 and the
stationary sleeve 56, as are upper and lower seal rings 66
and 68. The centers of gear 46, spacer 48 and peg wheel
44 are open to provide communication between sleeve 56 and
the inlet pipe 42.
A stationary supply pipe 70 receives compressed air from a
positive displacement type air pump 72 (see Fig. 1). The
end of pipe 64 opposite the pump 72 connects with an elbow
74 which is flanged at its lower end and connected to the
mounting plate 60 by bolts 76. The elbow 74 is
aligned with sleeve 56 in order to apply compressed air to
the sleeve and to the air accumulator tank 36 through its
inlet pipe 42. The rotary union 50 allows tank 36 to
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rotate about its vertical axis of rotation and at the sarne
time to continuously receive compressed air from the
stationary supply pipe 64.
The tank 36 is rotated by an electric motor 78 which
drives a speed reducer 80 bolted at 82 to the underside of
the mounting plate 60. The speed reducer 80 drives an
output shaft 84 which carries a pinion gear 86 that mates
with and drives the larger gear 46. The motor 78 is ener
gized continuously during operation of the air pulse
cleaning system and preferably drives tank 36 at a fixed
constant rotational speed selected within the range of
abou-t one half to two revolutions per minute.
The air that is accumulated in the tank 36 is applied
to the filter bags 30 by an air distribution arm 88 having
a plurality of discharge nozzles 89. Arm 88 is generally
horizontal and extends radially above tube sheet 14 from
one side of the air accumulator tank 36. The arm 88
tapers as it extends away from tank 36 and is flanged
at its inner end to connect with a flanged pipe 90 which
forms the inlet to arm 88. As best shown in Fig. 5, pipe
90 extends into the bottom portion of tank 36 and is
secured to the tank, as by welding. Pipe 90 is inclined
from horizontal and is provided with a horizontal
inle-t fitting 92 on the end opposite the flanged end. The
fitting 92 provides an inlet 94 to arm 88 which is located
within tank 36.
The discharge nozzles 89 are equal in number to the
openings 28 on each segment and are arranged on arm 88 in
the same pattern as the filter bag opening 28 are arranged
on each segment 22 of the tube sheet. Consequently, as
arm 88 rotates about the center of the tube sheet, nozzles
89 are successively aligned above the openings 28 in
each of the segments 22. Rach nozzle 89 preferably has
the same size as all other nozzles to apply cleaning
pulses with the same force from each nozzle.
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Numeral 96 generally designates a main diaphragm valve
which controls the entry of air through the distribution
arm inlet 94. A cylindrical housing 98 projects to one
side of tank 36. The housing 98 surrounds and is
concentric with the inlet fitting 92. An angle 100 is
welded or otherwise secured to the end of housing 98. A
valve head 102 covers the end of housing 98 and is secured
to the angle 100 by bolts 104. The bolts also secure the
periphery of a flexible diaphragm 106 between the angle
100 and valve head 102.
The flexible diaphragm 106 moves between the closed
position of Fig. 5 and the fully open position of Fig.
6~ In the closed position, a neoprene ring 108 forms a
seat which seals against the edge of the inlet fitting
92 to close inlet opening 94. The ring 108 is suitably
secured to the inner face of diaphragm 106. A circular
backing plate 110 is secured centrally to the outer face
of diaphragm 106 by a bolt 112 that engages a washer
114. Plate 110 is slightly larger in diameter than
fitting 94.
A tube 116 which projects from the valve head 102 receives
a coil spring 118. The spring 118 normally extends out of
tube 116 and is secured at its end to -the backing
plate 110. The force applied to diaphragm 106 by spring
118 continuously urges the diaphragm toward the closed
position. A circular bumper 120 is secured to the inside
surface of the valve head 102 and is engaged by the
backing plate 110 in the open position of the
diaphragm. In the open position, inlet 94 is fully
exposed so that air can pass through it into the
distribution arm.
The main diaphragm valve 96 is controlled by a
secondary diaphragm valve 122 which connects through the
valve head 102 with a pressure chamber 124 located between
the valve head and diaphragm. When the secondary valve
~2575~:Z
122 is closed, high pressure air is retained in the val~e
chamber 124 to cooperate with spring 118 in holding
diaphragm 106 in the closed position. The diaphragm 106
is provided with a series of small bleed holes 126 which
are located outside of the backing plate 110 and which
transmit high pressure air from tank 36 into the pressure
chamber 124. When the secondary valve 122 is opened, it
quickly exhausts the high pressure air from chamber 124,
and the pressure in tank 36 acts against the inner face of
diaphragm 106 and overcomes spring 118 to move the
diaphragm to the open position.
The secondary valve 122 is controlled by a pneumatic pilot
line 128 which is in turn controlled by a solenoid valve
130. As best shown in Fig. 3, the pilot line 128
connects with a threaded tube 132 through a pair of elbows
134 and a short vertical pipe 136. Pipe 136 extends
through aligned openings formed in the peg wheel 44 and
the large gear 46. Tube 132 is threaded into the body 52
of the rotary union 50 and communicates with an
annular chamber 138 formed between body 52 and the inner
sleeve 56 of the rotary union. A short nipple 140 is
fitted through sleeve 56 and is in communication with
chamber 138. The nipple 140 connects with the solenoid
valve 130 through a pair of pipes 142 and elbows
144. When the solenoid valve is closed, it maintains the
pressure in the pilot line 128 which in turn maintains the
secondary valve 122 in the closed condition. However,
when the solenoid valve 130 opens, the pressure in the
pilot line is exhausted and the secondary valve 122
opens to exhaust the pressure chamber 124 of the main
diaphragm valve.
The control system which actuates the solenoid valve 130
includes a proximity sensor 146. The proximity sensor
is mounted on a bracket 148 at a location adjacent to the
periphery of the peg wheel 44, as best shown in Fig. 4.
Extendiny downwardly from the lower face of the peg wheel
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44 near its periphery are a plurality of pegs 150 ~Ihich
are arranged in a circle centered on the rotational axis
of the accumulator tank 36. There are the same number of
pegs 150 as there are segments 22 on the tube sheet 14.
The pegs 150 are spaced equidistantly apart and are
located such that each time a peg is adjacent to the
proximity sensor 146, the distribution arm 88 is aligned
above the corresponding segment 22 with the discharge
nozzles 89 centered on the underlying openings 28 and
filter bags 30. The proximity sensor 146 is a
conventional unit which senses when a peg is adjacent to
it and generates an electrical signal each time it senses
the presence of a peg.
With particular reference to Fig. 7, a control box 152
mounted on the filter housing 12 receives electrical power
applied to a conductor 154. ~nother conductor 156 leads
from the proximity sensor 146 to a counter 158 located in
the control box 152. The counter 158 counts the
electrical signals generated by the proximity
sensor. When the counter is advanced to a preselected
count state (such as 3), it activates a pulse generator
160 located within the control box. The pulse generator
is electrically connected with the solenoid valve 130 by a
conductor 162. When activated by counter 158, the
pulse generator applies an output signal which opens the
solenoid 130. The counter 158 is reset each time it
activates the pulse generator 160.
In operation of the dust filter, a blower (not shown)
draws dust laden air or other gas into the dirty air
plenum 18 and through the filter bags 30 into the clean
air plenum 16 from which the filtered air is discharged.
The air pulse cleaning system of the present invention
operates to dislodge the dust which accumulates on the
outside surfaces of the filter bags 30 during the
filtering operation.
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As previously indicated, the drive rnotor 78 is
continuously energized to rotate tank 36 and the attached
distribution arm 88 at a constant rotational speed (one
revolution per minute, for example). As arm 88 rotates,
it is moved from one segment 22 to the next segment
and is aligned above the successive segments such that the
discharge nozzles 89 are momentarily centered on the
openings 28 and filter bags 30 of each segment 22.
Each time the arm 88 is aligned above one of the
segments 22, the corresponding peg 150 is adjacent to and
is sensed by the proximity sensor 146. The proximity
sensor then applies a signal to -the counter 158, and each
signal increments by one the count state of the counter
until its preselected count sta-te is reached. For
example, if a count state of three is selected, the third
peg 150 which reaches the proximity sensor 146 causes
counter 158 to activate on the pulse generator 160 and to
reset to zero. The pulse generator then applies a signal
to the solenoid 130 which opens the so~enoid valve to
exhaust the pilot line 128. The pressure reduction in the
pilot line in turn opens the secondary valve 122 to
exhaust air from the pressure chamber 124 of the main
diaphragm valve 96. Since compressed air is continuously
applied to the accumulator tank 36, the pressure in
the accumulator tank builds up to a sufficient level (such
as 7 psi) to open the diaphragm 106 by the time the third
peg 150 is sensed. When the pressure chamber 124 is
exhausted by the secondary valve 122, the pressure in tank
36 acting against the diaphragm 106 overcomes the
force of spring 118 and moves diaphragm 106 to the fully
open position shown in Fig. 6.
When the diaphragm opens, the compressed air in tank 36
quickly enters inlet 94 and flows through fitting 92
and pipe 90 into the distribution arm 88. The accumulated
air is discharged in a single sharp blast which is applied
through all of the nozzles 89 with substantially equal
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force. Since the nozzles 89 are at this time centered
over the openings 28 of the underlying segment 22, all o~
the air which is applied to the distribution arm 88 is
discharged through the filter bags 30 to dislodge
accumulated dust from the outside surfaces of the
bags.
The solenoid 130 is opened only momentarily. When the
pressure in the accumulator tank 36 drops sufficiently,
spring 118 returns diaphragm 106 to the fully closed posi
tion shown in Fig. 5. As the pressure builds up again
in the accumulator tank, air is able to bleed through the
bleed holes 126 into the high pressure chamber 124, and
the diaphragm remains closed until the solenoid valve 130
is opened again after three more pegs have been sensed by
the proximity sensor.
In this manner, the pulse cleaning system operates to
apply a single air pulse through each of the discharge
nozzles 89 each time arm 88 reaches the end of a
rotational increment. At the beginning of each cycle,
the diaphragm 106 of the main diaphragm valve closes and
pressure builds up in the accumulator tank 36 as the
distribution arm 88 rotates through the increment covered
during the cycle. The pressure continues to build in the
accumulator tank until the distribution arm 88 has
passed over two segments 22 and is aligned above the third
segment at the end of the increment. Then, the control
system opens the solenoid 130 and the secondary valve 122
and main valve 98 in rapid succession to apply air pulses
to the filter bags through the discharge nozzles 89.
In order to provide sufficient time for the pressure to
build up to tha required level in the accumulator tank 36,
and to minimize redeposition, it is preferred to clean
only the third of the filter bags 30 during each full
revolution of the distribution arm 88. Another one third
of the filter bags are cleaned during the next revolution,
14
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and the final one third are cleaned during the third
revolution. Thus, each filter bag is thoroughly and
assuredly cleaned during every three revolutions of the
distribution arm.
All of the filter bags 30 are cleaned in a unifonn manner
because each bag is pulsed with the same frequency (once
for every three revolutions of the distribution arm~ and
the air pulses are applied with approximately the same
10 force from all of the discharge nozzles 89. Also, all
of the air pulses that are applied by nozzles 89 are
applied directly to the centers of the filter bags, and
none of the pulses are wasted. The result is that
virtually all of the compressed air is used for cleaning
15 of the bags, and the system thus operates more
efficiently than systems which apply significant amounts
of air against the surface of the tube sheet.
The accumulator tank 36 and the main valve 96 are combined
in a single unit which is located adjacent to the
inlet end of the distribution arm 88. This arrangement
minimizes the response time because the compressed air
surrounds the inlet 94 and is thus already close to arm 88
at the time the diaphragm 106 is opened. A fast response
time is essential if the air is to be discharged from
the nozzles 89 while the nozzles remain in alignment with
the underlying openings 28. The quick acting nature of
the valve system also eliminates undue delay between
proper positioning of the distribution arm and discharge
of the air pulses. The close proximity of the
accumulator tank and valve to the distribution arm has the
additional benefit of minimizing flow losses. The
compressed air enters inlet 94 direc~ly from the
distribution tank and flows to the arm in a substantially
straight line path to avoid appreciable loss of air
and resulting inefficiencies. It is also noted that the
annular space between fitting 92 and housing 98 contains a
large volume of compressed air to avoid unduly restricting
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the air flow from the tank into the distribution arm~
In addition to the foregoing advantages, the sturdy
accumulator tank 36 forms a structural part of the
rotation system for the distribution arm.
Consequently, the tank enhances the structural integrity
of the rotation system and eliminates the need to use
additional structural members to provide the rotation
system with the necessary strength.
From the foregoing, it will be seen that this invention is
one well adapted to attain all the ends and objects
hereinabove set forth together with other advantages which
are obvious and which are inherent to the structure.
It will be understood that certain features and
subcombinations are of utility and may be employed without
reference to other features and subcombinations. This is
contemplated by and is within the scope of the claims.
Since many possible embodiments may be made oE the
invention without departing from the scope thereof, it is
to be understood that all matter herein set forth or shown
in the accompanying drawings is to be interpreted as
illustrative and not in a limiting sense.
